Duo self-hosted BYOM authentication iteration 1: Token auth with GitLab AIGW
## Description
For iteration 1, we will use token authentication via the existing `api_token` field the on the `ai_self_hosted_models` table.
The roadmap for [provider support](https://gitlab.com/groups/gitlab-org/-/work_items/20499#note_3021687230) is in this (preferred) order:
> 1. Bedrock (parity with current functionality)
> 2. Azure (parity with current functionality)
> 3. Vertex (popular platform with many models)
> 4. Anthropic and OpenAI (for customers using API's directly from Anthropic and OpenAI)
Token authentication is supported by Bedrock, Azure, OpenAI and Anthropic – but not Vertex. Vertex support will come in [iteration 2](https://gitlab.com/groups/gitlab-org/-/epics/20824) when we implement support for temporary credentials.
### BYOM with tokens UX
See [comment](https://gitlab.com/groups/gitlab-org/-/epics/20463#note_3046586170) for more context
| BYOM model creation form | Recording |
|--------------------------|-----------|
| {width="702" height="600"} | {width="666" height="600"} |
epic